Answer:
(C) is the mechanism that increases the temperature between the photosphere and corona of the sun.
Explanation:
When a stars is converted from hydrogen to helium then this is known as proton -proton chain reaction.Due to this reaction the temperature between corona of the sun and photosphere increases.The main reason for increasing the temperature is exothermic reaction.
So the option C is correct.
(C) is the mechanism that increases the temperature between the photosphere and corona of the sun.